Synchronized motor



Nov. 7, 1939. T. A. REID 2,179,350

SYNCHRONI-ZED MOTOR Filed April 10, 1937 WITNESSES: IVNVENTOR wwfia Thames fl Qez'd,

BY 67/4. 5. M fl Patented Nov. 7, 1939 @llainos.

This invention relates to systems of control for motors, more particularly'to systems of control for maintaining two or more direct current motors in synchronism.

Devices and systems of control have heretofore been known for maintaining two or more alternating current electric motors in synchronisrn, and the principles used with some of such motors have also been used to maintain synchronous operation of two or more direct current motors. With the devices of the prior art, motors could be maintained in synchronism once the motors were up to their normal operatin speed, synchronous acceleration could not he secured nor could such motors be electrically looked and. maintained in proper relation at zero speed.

One object of my invention is to lock two or more motors in proper relation at zero spec,

Another object of my invention is to clot and maintain a stationary and rotating lnterlock between two or more direct current ino'ors.

It is also an object of my invention to Bob: and maintain a stationary interlock between. or more direct current motors.

A still further object of my inve tain and maintain a selected corresponding points on the rotat of two'or more direct current motors of the speed of such elements.

Other objects and advantages will become apparent from a consideration of the following specification and the claims thereto appended the accompanying drawing, in which, the single figure constitutes a diagrammatic showing of pair of direct current motors controlled with my system of control which is also shown dia grammatically.

My system of control is particularly adaptable to the simultaneous and synchronous recording of sound and pictures in the motion picture in dustry. My invention is, however, not limited to th s field but may be applied in many industrial applications and also be used in other motion picture work such as back ground projection, where it is necessary to electrically interlock the projection machine and the camera at standstill, or in re-recording or other work requiring the interlocking of two or more pieces of apparatus.

Generally, my system consists of two or more direct current motors each driving its own piece of apparatus such as a camera and a recorder. The armature of each direct current motor is tapped with three leads spaced 120 electrical de grees apart and these leads, through slip-rings and brushes are connected together in proper phase relation as a three phase synchro-tie connection. This much of the system constitutes a running or rotating interlock due to the alternating current voltage developed in the motors and impressed on common conductors.

In an effort to get a standing interlock, I discovered that the application of an alternating current voltage to the leads or connections between one pair of slip rings namely, across one phase, provides such standing interlock. The alternating current thus applied to the slip rings may as of commercial frequency and voltage be left connected to the leads, or conrconnecting the slip rings during c of operation, that is, for successive complete cycles of operation ranging from and including zero speed of the motors up to speed.

the reference designates a motor of the direct-current lch to he maintained in synchronism actor 53. For the purposes of this speci hall consider the word synchronous connected to a load 3 -lesignated camera load, whereas ed a load which may he corder load. These motors are alike city and e sign and they will have the sa rig and other wise the same mechani cal and, as near as possible, the same electrical characteristics and are also of the rotary con verter type, which have a commutator at one end and three slip rings at the cither end of the rotor, the slip rings being connected to the Q1319, ture winding at three points spaced 120 electrlcal degrees apart. These motors may, in general, he considered as designed for operation on volt direct current circuits.

It will be noted that the slip rings shown at the alternating-current ends of the motors are interconnected by leads 5, 6 and l, the inter connection being such that if the rotors have corresponding mechanical phase positions, the windings will be interconnected also to have like electrical phase relation, if these motors be considered as in operation, namely, both of them driving their loads. If there be a tendency on one of the motors, by reason of a variation of its load or any other reason, to pull out of synchronism, the current circulating in the leads 5, 6 and l will maintain synchronous operation. This interconnection of the armature windings is known as a synchro-tie connection. If the motors are stopped and one rotor should drift farther than design the other, the motors will upon the second starting, operate in such a manner as to have the same period, but they will not be in synchronism in the sense that the rotors will also have corresponding phase positions. F'urther, if these motors are operated at variable speed, the synchronous operation may be lost although the motors ,will operate in such a manner as to have the same period. For apparatus used in the motion picture industry of a semi-portable character or for news-reel work or for use on location and various other types of work where it is dimcult to maintain constant speed and very often not desirable to maintain constant speed of the motors, such failure on the part of two or more motors to operate in predetermined synchronism may be quite detrimental to the proper taking oi. pictures and the recording of sounds.

With my system of control, I provide a single phase source of alternating-current evidenced by the transformer 8. The secondary of the transformer is provided with a number of leads or taps so that the voltage taken from the secondary may be varied at will. This single-phase source of alternating current I interconnect with two of the leads 5 and 6, as shown, through the contact members 9 and III of an electromagnetic switch II. The electromagnetic switch I I also controls a starting contactor I2 for energizing the motors I and 2 with direct-current. Neither electromagnetic switch Il nor the starting contactor I2 are absolutely necessary in the particular arrangement I have shown. It is sufficient to obtain the novel results of my invention that a source of alternating-current of suitable voltage be available for interconnection with the leads 5 and 3 and that a suitable source of direct-current be available for interconnection with the armatures and field windings of the motors l and 2, respectively. Furthermore, it is not essential that the voltage taken from the secondary of the transformer 8 be adjustable. Broadly, the novel results of my invention are attained ii the camera and the recording mechanism are brought in proper phase relation and then the leads interconnecting the slip rings be energized with a single-phase alternating-current. Under this condition that is, the instant the leads are energized with alternating-current, the two motors if not quite in correct position jump into correct phase position and the voltage generated in the fields, which will at such time as shown in the drawing be connected in parallel, will build up and be directly opposed. The motors I and 2 will thus be firmly interlocked and held in a given position; that is, corresponding points on the rotors will be maintained in a given position with reference to each other even though the motors are at rest. The direct-current may thereafter be applied to the motors and the motors brought up to normal speed. The motors will thus operate in synchronism throughout the period of acceleration from and including the zero speed up to the normal speed of the motors.

A still better understanding of my invention can probably be had from a study of a typical cycle of operation. Assuming that the motors I and 2 are at rest and not energized at all, and it is desired to start the camera and the recorder and thereafter maintain synchronous operation for successive cycles of operation as well as variations in speed of the motor. Assuming further that the busses designated at It and I1 are suitably energized with direct-current and that the transformer 8 is energized from a suitable source of alternating current. To start the operation of my system of control, the attendant makes certain that switch 1' is open and then actuates the starting switch I3, thereby establishing a circuit from the positive direct-current bus I4 throughthe starting switch I3, actuating coil I5 of the electromagnetic switch l1 and stop switch It to the negative conductor I1. As soon as the actuating coil I5 is energized, contact members 3 and III are closed whereupon the motors have two oi! the leads, namely, 5 and 6, oil the synchro-tie connection energized with a single-phase of alternating-current of suitable voltage and the motors immediately look into a given position. Switch 1' may be open while motors I and 2 are at rest, but should be closed when the motors are running.

Operation of electromagnetic switch II also causes the closing of contact members I8, which contact members merely establish a holding circuit for the actuating coil Ii, so that the attendant may -release starting switch I3. Contact members It are also closed. The closure of contact members It merely makes it possible to energize the motors I and 2 by a suitable operation of the starting contactor I2.

To start the operation of the motors I and 2 the attendant actuates the switch 20, whereupon a circuit is established from the positive conductor I4 through contact members I9, switch 20 and actuating coil 2I of the starting contactor I2 to the negative bus l1. The operation of the starting contactor I2 causes the closing of contact members 22 whereupon a circuit is established from the positive bus I3 through the upper contact member 22,.conductor 23, field windings 25 and 23 connected in parallel and the lower contact member 22 to the negative bus I1. A circuit is also established by the operation of the starting contactor I2 for the armatures oi the motors I and 2. It will be noted that conductor 23 is directly connected to the upper terminals, or brushes 21 and 23, oi the motors I and 2, respectively. The lower brushes 23 and 3B of motors I and 2 are connected to the arm 3I of a starting rheostat 33 through several sections of the starting rheostat 33 to conductor 34 and through the lower contact member 22 to the nesative bus I1.

At the time of operation of the electromagnetic contactor I2, the rheostat arm 3| should be in such a position as to include the maximum amount of resistance in the armature circuit oi the respective motors. In fact, arm 3I could be in such a position as to still maintain the armatures of the motors on open circuit. Whichever the position may be, the attendant will actuate handwheel 31 rotating it so that the nearer portion of the wheel moves downwardly, thereby causing the arm 3| oi the rheostat .33 to move counter-clockwise. It will thus be apparent that both motors I and 2 simultaneously have their voltage increased and will thus increase their speeds to any value desired.

It should be noted that the handwheel 31 also actuates the voltage adjusting arm 32, cooperating with the secondary of the transformer 3. It has been found that best results are secured ii the single-phase alternating-current voltage is maintained approximately equal to the voltage generated by the motor in one of the phases of the armature windings. The arm 32 is, as shown, interconnected mechanically with the handwheel 31, so that as the speed of both motors increases, the alternating-current voltage impressed on the alternating-current leads of the motors will also be increased. As indicated, the arm 32 will move counter-clockwise with an increase of speed of the motors. It should be noted, 5 however, that when the speed of the motors is decreased, that is, namely, when arm 3i moves clockwise arm 32 moves counter-clockwise. The design should, however, be such that the voltage of the secondary of the transformer 8 is not de- 10 creased to zero but should be maintained at a value sufliciently high to obtain and maintain the interlocking of the rotors of the motors i and 2 even at zero speed. In other words, the alternating-current voltage impressed on the synchro-tie leads 5 and 6 should not, during the entire operation of the motors, be reduced to zero.

Once the motors, and thus the loads connected to the motors, have been synchronized,

the attendant may start and stop the motors by suitable manipulation of the handwheel 31 without at any time losing the interlocked relation of the two motors and the loads connected to them. The motors will stop when the armatures are disconnected at the rheostat 33, but will remain locked in a given phase position and then when the rheostats are operated, the motors will operate in synchronism without of course having lost the proper phase relation. Regardless of the variation of the voltage and thus the speed of the motors, the motors will operate with the same period and the same phase position, maintaining such phase position whether in operation or at rest.

a While I have shown electromagnetic starting means which are so arranged that the alternating current is supplied to the motors before the direct-current can be connected to the motors, and while I have shown certain voltage control 49 for the alternating current to be supplied to the motors as well as certain voltage control for the direct-current voltage to be supplied to the armatures of the motors, I do not limit myself to the specific. showings made. As a matter of fact, no

5 voltage adjustment for the alternating current to be supplied to the motors need be provided at all, provided the original selection of the voltage value is correct. Such selected voltage value may be a trifle larger than needed at very slow 50 speeds or at zero speed but the losses are not appreciable and may 'thus be disregarded. Similarly, the rheostats 33 and 36 need not necessarily be provided. Any suitable switching means and starting control for the motors will suflice so long 50 as the attendant maintains the proper order of starting the two motors; namely, of energizing them with alternating-current first after the proper phase position for the rotors has been selected and .thereafter simultaneously energizing the motors with direct-current. For small ma-. chines, such simultaneous energization may frequently mean full voltage starting, thus eliminating the need of starting rheostats. 5

I am, of course, aware that others particularly after having had the benefit of the teachings of my invention, may readily devise other circuit diagrams or other means for accomplishing the novel results I have disclosed in this application 10 and I, therefore, do not wish to be limited to the specific showing nor the specific description given but wish to be limited only by the scope of the appended claims and such prior art as may be pertinent. 15

I claim as my invention: 1. In a system of control for electric motors, in combination, a pair of direct-current motors having their armature windings and field windings connected in parallel, synchro-tie connec- 20 tions between the armature windings, a source of alternating current, a source of direct current, means adapted to connect said source of alter nating current to said synchro-tie connections, means adapted to simultaneously connect said 25 armature windings and field windings to said source of direct current, and means for simultaneously varying the voltages applied to said motors of said source of alternating current and said source of direct current. 30

2. In a system of control for electric motors, in combination, a pair of direct-current motors having armature windings and field windings all connect-ed in parallel, synchro-tie connections between the armature windings, a source of single phase alternating current, a source of direct current, and electromagnetic control means adapted to connect said single phase source of alternating current to said synchro-tie connections and thereafter automatically connect said 40 source of direct current to said armature windings and said field windings.

3. In a system of control for electric motors, in combination, a pair of direct current motors having armature windings and field windings all connected in parallel, synchro-tie connections between the armature windings, a. source of single phase alternating current, a source of direct current, electromagnetic control means adapted to connect said single phase source of alternating 60 current to said synchro-tie connections and thereafter automatically connect said source of direct current to said armature windings and said field windings, and means for simultaneously varying the voltages of the said sources of current applied to the said motors.

. THOMAS A. REID. 

